Means for improving constant voltage transformers



Feb. 22, 1966 L. DUBIN ET AL 3,237,089

MEANS FOR IMPROVING CONSTANT VOLTAGE TRANSFORMERS SATURABLE 7YPE Filed June 21, 1961 INVENTORS LESTER DUBIN SOL GREENBERG BY RAYMOND HASTINGS ATTORNEYS United States Patent C) 3,237,089 MEANS FOR IMPROVING CONSTANT VOLTAGE TRANSFORMERS Lester Dubin, Pelham Manor, Sol Greenberg, Port Washington, and Raymond Hastings, Plainview, N.Y., assignors to Lambda Electronics Corporation, Huntington,

N.Y., a corporation of New York Filed June 21, 1961, Ser. No. 118,640 2 Claims. (Cl. 323-44) This invention relates to improvements in transformers of the constant voltage type and, more particularly, to improvements in A.C. saturable type constant voltage transformers also known as voltage stabilizers and A.C. line voltage regulators.

Transformers of this type are designed to provide regulation, and they find wide application in electrical equipment, for example, in regulated DC. power supplies.

To achieve such regulation, these transformers employ, in addition to the basic components, a capacitor in combination with a saturable inductance which combination is tuned to the region of the operating frequency. Relatively large amounts of copper (in the windings) and iron (in the core) are also required. The cost of these materials, the bulk they add to the transformer, and the extra costs of processing, handling and shipping, all contribute substantially to the overall cost. As a result, these transformers in many applications can not compete with functionally equivalent arrangements.

It is, accordingly, an object of the invention to provide methods and means for improving constant voltage transformers in which for given ratings such as VA and temperature rise, a substantial reduction in the size and weight of the transformer is effected.

A further object of the invention is to provide methods and means for reducing the size and weight, and, therefore, cost, of constant voltage transformers without reducing the ratings or substantially impairing the performance thereof.

A still further object of the invention is to provide an improved constant voltage transformer in which for given ratings such as VA and temperature rise, a smaller resonating capacitor may be used.

A still further object of the invention is to provide constant voltage transformers having higher VA-to-weight ratings than heretofore achieved.

These and other objects and advantages of the invention will be set forth in part hereinafter and in part will be obvious herefrom, or may be learned by practice with the invention, the same being realized and attained by means of the steps, methods, combinations and improvements pointed out in the appended claims.

Briefly and generally, the invention comprises the addition of resistance to, and the reduction of capacity in, the LC combination of a saturable type constant voltage transformer.

The invention consists in the novel steps, methods, parts, constructions, arrangements, combinations and improvements herein shown and described.

Serving to illustrate and explain exemplary embodiments and methods of the invention are the drawings, of which:

FIGURE 1 is a schematic diagram of a circuit useful in explaining the operation of saturable type constant voltage transformers;

FIGURE 2 is a schematic diagram of a saturable type constant voltage transformer constructed according to the invention; and

FIGURE 3 is a plan view of a core configuration employed in a transformer constructed in accordance with the invention.

3,237,089 Patented Feb. 22, 1966 While saturable-type constant voltage transformers differ in detail in the use of compensating windings, special gaps, etc., and in core configuration and winding interconnection, they nevertheless reduce in essence to an equivalent circuit which includes a series inductance L and a parallel LC branch effectively in shunt relative to the load. A circuit of this general type is shown in FIG- URE 1 in idealized form. The circuit yields an output voltage 2 and is supplied by an input voltage 12,.

Inductance L is non-linear and thus introduces a nonlinear impedance into the circuit which, with proper choice of component values, provides the requisite regulation.

It has been found that the size and weight of saturable transformers can be substantially reduced by adding resistance to the transformer circuit and by decreasing the value of capacitance. While this step ostensibly adds an additional source of dissipation to the transformer, it has been demonstrated that the total losses do not, in fact, increase While, at the same time, the amount of copper and iron can be reduced by a substantial amount. While the precise theory explaining this phenomenon is not fully understood, it has been determined that (l) a reduction in capacitance alone reduces transformer losses, thus permitting a reduction in transformer size, but aggravates instability particularly under no-load conditions; (2) this deterioration in stability can be secured by adding resistance (lumped or distributed) so that it effectively acts in the LC circuit; (3) the addition of resistance restores a part, but not all, of the losses eliminated by the reduction in capacitance but a substantially smaller size transformer nevertheless results. Moreover, this additional resistance may be lumped externally of the windings and this is of particular advantage when it is recalled that the permissible operating temperature rise of the external resistance can be many times higher than the allowable temperature rise of the transformer windings. The reduction in capacity also effects a gain especially since typical values in known arrangements are rather large, e.g., 20 mfd.

Illustrating a practical embodiment of the invention is the transformer arrangement of FIGURE 2. An input terminal P adapted for connection to a source of alternating power, e.g., v., 60 c.p.s., is connected to one side of inductor L on a core 9. The other input terminal P is connected to one end, terminal 10, of a winding L on a core 15 of transformer T. The other end terminal 11 of winding L is connected to the series combination of capacitor C and resistance R with the other side of R being connected to the junction of terminals P and 10. An intermediate point of winding L connects via terminal 12 to the other side of inductor L The above arrangement provides auto transformer action and is similar to the arrangement wherein winding L actually comprises a plurality of electrically isolated windings, one of which has the R-C circuit connected across it.

In the circuit of FIGURE 2 the L C, R combination has a reactance which depends on the amplitude of the input voltage applied at terminals P and P the inductance of L being non-linear. This reactance, in varying with respect to the reactance of inductor L provides regulation in transformer secondary voltage.

Various secondary or output windings L L L and L is rectified and filtered to provide bias for various conpurposes depending on the transformer application. Thus, winding L is employed in one application to feed a load energized by a full wave bridge recifier (not shown); L serves as the alternating current source for a circuit employed to develop a reference voltage; the voltage at L is rectified and filtered to provide bias for various control elements such as transistors; L may drive a similar 1 Quantities referred to are vectoral.

Core 15:

Laminations E-I, 2%, interleaved 1 x l AISI MG, Ga. 29 (0.014). Stack height 3 Windings:

L 69 /2 turns (22 per layer, 3 /2 layers).

AWG 15, 2 in parallel. 0.005" interlayer insulation. 2% Winding traverse. Resistance=0.11 ohm (69).

L 233 /2 turns (52 per layer, 4%

layers). AWG #17. 0.005" interlayer insulation. 2% winding traverse. Resistance:l.35 ohms (267'). L 168 turns AWG 16 (46 per layer, 4

layers). AWG #16. 0.005 interlayer insulation. 2%" winding traverse. Resistance=0.88 ohm (218'). Resistor R 6 ohms (54 watts, max. dissipation). Capacitor C 8 mfd., 600 volts A.C. Inductor L 0.04 henry, 7 amps. operating current.

The above specifications are designed to meet particular operating conditions and values will accordingly vary under different conditions.

While a specific method and embodiment have been illustrated and described, further modifications such as those suggested by circuit equivalence, e.g., conversion of lumped to distributed parameters, conversion of series resistance to equivalent shunt resistance, the use of duality, and the like, will occur to those skilled in the art; it should accordingly be understood that the invention is not limited to the specific form and method shown but departures may be made therefrom within the spirit and scope of the invention as set forth in the accompanying claims.

What is claimed is:

1. In a constant voltage transformer circuit, the com bination of a saturable transformer core; a primary winding operatively associated with said core and having end terminals and a tap terminal therebetween; an inductance; circuit means connected to one of said end terminals and said tap terminal for serially coupling a portion of said primary winding to an A.C. source, via said inductance; a capacitor connected between said' end terminals having a capacitance value less than that normally required to achieve satisfactory constant voltage operation; a resistor connected in series with said capacitance between said end terminals having a value suflicient to eliminate no-load instability; and at least one output winding operatively coupled to said core.

2. A constant voltage transformer in accordance with claim 1 wherein said inductance is connected directly to said tap terminal.

References Cited by the Examiner UNITED STATES PATENTS 1,985,634 12/1934 Fleming 32360 2,143,745 1/1939 Sola 32360 2,432,343 12/ 1947 Short 323-60 2,505,620 4/1950 John et al. 323 2,530,011 11/1950 Forssell 32361 X FOREIGN PATENTS 1,125,127 7/1956 France.

583,497 12/ 1946 Great Britain.

LLOYD MCCOLLUM, Primary Examiner.

ROBERT C. SIMS, Examiner. 

1. IN A CONSTANT VOLTAGE TRANSFORMER CIRCUIT, THE COMBINATION OF A SATURABLE TRANSFORMER CORE; A PRIMARY WINDING OPERATIVELY ASSOCIATED WITH SAID CORE AND HAVING END TERMINALS AND A TAP TERMINAL THEREBETWEEN; AND INDUCTANCE CIRCUIT MEANS CONNECTED TO ONE OF SAID END TERMINALS AND SAID TAP TERMINAL FOR SERIALLY COUPLING A PORTION OF SAID PRIMARY WINDING TO AN A.C.COURCE VIA SAID INDUCTANCE A CAPACITOR CONNECTED BETWEEN SAID END TERMINALS HAVING A CAPACITOR VALUE LESS THAN THAT NORMALLY REQUIRED TO CHIEVE SATISFACTORY CONSTANT VOLTAGE OPERATION; A RESISTOR CONNECTED IN SERIES WITH SAID CAPACITANCE BETWEEN SAID END TERMINALS HAVING A VALUE SUFFICIENT TO ELIMINATE NO-LOAD INSTABILITY; AND AT LEAST ONE OUTPUT WINDING OPERATIVELY COUPLED TO SAID CORE. 